This invention relates to the manufacture of hydrodynamic seals from polytetrafluoroethylene and the like. It also relates to a die used therefor.
Polytetrafluoroethylene is a material which is not readily molded, as are the various synthetic rubbers, but which has some very desirable characteristics. In some uses, its ability to withstand high temperatures recommends its use as the oil sealing element which is in rotary contact with the shaft, instead of using one of the less temperature resistant synthetic rubbers. There are also other uses where this material would be advantageous, but heretofore its use has been greatly limited by its inability to be molded to desired shapes in an efficient manner. Normally, it has to be sliced or stamped out from sheets or otherwise formed as a thin washer-like member rather than being molded into any desired shape. Therefore, it is expensive to manufacture, and this expense has greatly limited its use.
The difficulty of molding this material has also made it impractical heretofore to make a hydrodynamic seal from polytetrafluoroethylene. Hydrodynamic seals have conventionally been made by molding a spiral groove or other hydrodynamic structure into the molded element. The washers have been difficult to handle, and such molding of polytetrafluoroethylene has been economically, at least, unfeasible.